1. Field of the Invention
The present invention relates to a dynamic cell reconfiguring method and a cellular network system to which the method is applied. More particularly, the present invention relates to a method of dynamically switching sector antennas to reconfigure cells adaptively to a traffic situation, and a cellular network system to which the same is applied.
2. Description of the Related Art
FIG. 1 shows a cell configuration in a cellular network system used widely throughout the world in general.
In FIG. 1, each circle represents a service area of a cell. A divided part of each circle shows a range covered by each sector antenna in the cell. The range covered by the sector antenna constitutes of a small independent area called a sector.
The sector is not affected by other network portions. In an example of FIG. 1, one cell is divided into six sectors, and each sector is independent of other sectors. The number of the sectors is not limited to six, and the cell is often divided into three sectors.
Because of the characteristic and applicability of the sector antenna, the cell can be divided into a large number of sectors, such as nine or twelve sectors.
In FIG. 1, a conventional cell configuration is the same in a business zone and a residence zone. All the cells include wireless devices and these wireless devices are installed in buildings or movable shelters.
As shown in FIG. 2 describing changes in a traffic amount over time, peak usage is at different moments depending on situations. A business zone I and a residence zone II have opposite tendencies at same hours during the day.
In the business zone I, the usage is high at daytime business time zone III and the usage is low in the nighttime. Contrary, in the residence zone II, the usage is low at daytime zone III and the usage is high in the nighttime.
When a network system is constructed, a peak time zone is found out when network is most busy and a traffic amount at that time zone is determined to decide the number of installed base stations. This means that network apparatuses are provided to maintain the quality of the service such that no call is lost or discontinued in the busiest time zone.
People work in the daytime and go home in the nighttime. The business zone is almost empty in the nighttime. Therefore, the network in the residence zone has an excessive capacity in the daytime and the network in the business zone has an excessive capacity in the nighttime. These excessive capacities increase costs of the network.
In such a network configuration, typically, it is acceptable a quality of the service to the extent that in 100 calls in a mobile network or one or two calls are lost in handover operation or at initial connection. The handover corresponds to path connection of a communication link from one cell to another cell.
However, since the cellular network looking at this operation property based on human migration, the cellular network includes the possibility of reducing total costs.
Prior art eliminating unbalance in communication capacities depending on time zones includes an invention described in Japanese Patent Application Laid-Open Publication No. 2001-128227. The invention described in Japanese Patent Application Laid-Open Publication No. 2001-128227 is a mode of controlling an electric wave radiation directivity, etc. of a base station depending on a base station state pattern table maintained and managed in a switching equipment based on the premise of maintaining and managing the base station state pattern in the switching equipment and the premise of that the base station can change the electric wave radiation directivity, transmission power, and receiver sensitivity, and the domain of applicability is array antenna control.
Another technology is an invention described in Japanese Patent Application Laid-Open Publication No. 1994-153256. The purpose of the invention described in Japanese Patent Application Laid-Open Publication No. 1994-153256 is to change the number of carriers used in a cell depending on traffic of each cell. This mode is provided with an optical switch and changes a connected cell with an optical cable. The cell configuration itself is “fixed”. That is, only the number of carriers assigned to a cell is changed depending on traffic.
In the technologies eliminating unbalance of communication capacities depending on time zones shown in FIG. 2, the domain of applicability of the invention described in Japanese Patent Application Laid-Open Publication No. 2001-128227 is limited to array antenna control, and the amount of equipment such as installed base stations is not expected to be reduced in the invention described in Japanese Patent Application Laid-Open Publication No. 1994-153256.
Although traffic amounts of the day and night are actually varied in each region and the difference between the daytime and the nighttime is especially significant in a business block and a residential block, in a conventional method, equipment such as base stations has been installed such that the maximum traffic of the region can be supported. Therefore, wasted capital investments must be provided and this is a problem in the aspect of effective utilization of equipment.